WASHINGTON -- Alarmed by the shooting attack on a Silicon Valley-area power station last spring, several senators called on regulators to review security operations at electrical utilities and consider imposing new rules to protect against future attacks.

“Last year’s sophisticated attack on the Metcalf substation in California’s Silicon Valley was a wake-up call to the risk of physical attacks on the grid,” said a letter the senators sent regulators Friday. “The incident came uncomfortably close to causing a shutdown of a critical substation which could have resulted in a massive blackout in California and elsewhere in the West.”

The letter was signed by Senate Majority Leader Harry Reid of Nevada and fellow Democratic Sens. Dianne Feinstein of California, Ron Wyden of Oregon and Al Franken of Minnesota. It was addressed to executives at the Federal Energy Regulatory Commission and the North American Electric Reliability Corp., an industry group that sets rules for how power companies operate.

The April shooting at a Pacific Gas & Electric Co. facility was originally downplayed by authorities as an act of vandalism. It had attracted little congressional interest until this week, when a former top power regulator offered a more chilling interpretation. He said the attack was terrorism.

Jon Wellinghoff, who was chairman of the Federal Energy Regulatory Commission when the shooting took place, said it was clearly executed by well-trained individuals seeking to do significant damage. He expressed concern it could have been a test run for a larger assault that could knock out power in a swath of the country for an extended period of time. FBI officials say they do not believe a terrorist organization was involved, but they have made no arrests and named no suspects.

The letter from the senators comes as Congress has been wrangling for years over rules for protecting the nation's power grid. Proposals to give regulators more authority to impose security measures have languished amid resistance from power companies. The senators suggested in their letter that a provision of existing law authorizes regulators and the Electric Reliability Corp. to create mandatory rules to protect against cascading blackouts threatened by a “sudden disturbance.”

“A physical attack on the bulk power system certainly falls comfortably within that definition,” the letter said.

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